Beam-steering System Based on a MEMS-Actuated Vertical-Coupler Array

ABSTRACT

An integrated-optics MEMS-actuated beam-steering system is disclosed, wherein the beam-steering system includes a lens and a programmable vertical coupler array having a switching network and an array of vertical couplers, where the switching network can energize of the vertical couplers such that it efficiently emits the light into free-space. The lens collimates the light received from the energized vertical coupler and directs the output beam along a propagation direction determined by the position of the energized vertical coupler within the vertical-coupler array. In some embodiments, the vertical coupler is configured to correct an aberration of the lens. In some embodiments, more than one vertical coupler can be energized to enable steering of multiple output beams. In some embodiments, the switching network is non-blocking.

CROSS REFERENCE TO RELATED APPLICATION

This case is a continuation of co-pending U.S. patent application Ser.No. 17/252,671, filed Dec. 15, 2020 (Attorney Docket: 332-007US1), whichis a national-stage application of International Application No.PCT/US19/37973, filed Jun. 19, 2019 (Attorney Docket: 332-007WO1), whichclaims the benefit of U.S. Provisional Patent Application Ser. No.62/686,848, filed on Jun. 19, 2018 (Attorney Docket: 332-007PR1), eachof which is incorporated herein by reference.

If there are any contradictions or inconsistencies in language betweenthis application and the cases that have been incorporated by referencethat might affect the interpretation of the claims in this case, theclaims in this case should be interpreted to be consistent with thelanguage in this case.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with Government support under Contract No.DE-AR0000849 awarded by the Advanced Research Projects Agency-Energy(ARPA-E). The Government has certain rights in the invention.

TECHNICAL FIELD

The present disclosure relates to free-space optics in general, and,more particularly, to free-space beam-steering.

BACKGROUND

Agile beam-steering devices are needed for free-space opticalcommunications as well as LiDAR (light detection and ranging), 3Dimaging, sensing, and microscopy applications. They provide scanning andacquisition/pointing/tracking (ATP) functions. Traditional beam-steeringapparatuses use motorized mechanical gimbals to rotate the entireoptical systems. Unfortunately, motorized gimbals are bulky, heavy, andconsume a great deal of power.

Integrated beam-steering systems have shown great utility in portable ormobile platforms, and have become key elements of “solid-state LiDAR”.For example, collimation and beam-steering has been demonstrated in theprior art using a light source positioned at the focal plane of a lens(e.g., telecentric lens, telescope, etc.) and changing the arrangementof the position of the optical axis of the lens and the position of thelight source within the focal plane of the lens. This has been done invarious ways, such as by moving a macro light source relative to theoptical axis, moving an optical fiber located in the focal plane, andmoving the lens relative to a fixed-position light source.

Unfortunately, the mechanical systems required to move the lens and/orlight source have limited frequency response due to the weight/stiffnessof the loads, are too slow for LiDAR and/or free-space communicationsbetween fast moving vehicles, and are bulky, complex, slow, andexpensive.

Other prior-art beam-steering systems are based on electronic crossbarswitches that selectively energize individual elements of atwo-dimensional (2D) array of vertical cavity surface-emitting lasers(VCSEL). However, such an approach requires large arrays of lasers. Inaddition, such systems require VCSEL sources, which are not well suitedfor some communication or sensing applications.

Still other prior-art beam-steering systems have usedsilicon-photonic-based thermo-optic switches to activatesurface-emitting grating couplers. Unfortunately, thermo-optic switchesare temperature sensitive, have limited steering capability, have highpower consumption and do not scale well to large-scale beam-steeringdevices.

Practical beam-steering technology remain, as yet, unavailable in theprior art.

SUMMARY

The present disclosure is directed to a beam-steering apparatuscomprising an integrated-optics-based, programmable, two-dimensional(2D) array of mechanically active vertical-grating couplers (i.e.,couplers) that is located in the focal plane of a lens. The lens isarranged to convert free-space light emitted by any of the couplers intoa collimated, free-space light beam. The programmable coupler array ismonolithically integrated on a substrate and includes a switchingnetwork that controls which coupler (or couplers) is energized (i.e.,receives light and launches it into free space). The switching networkis configured to mitigate leakage to non-energized couplers, therebymitigating optical crosstalk. The propagation direction of eachfree-space light beam (i.e., its output angle with respect to theoptical axis of the lens) is a function of the x and y coordinates ofits respective coupler relative to the optical axis of the lens.Embodiments in accordance with the present disclosure are particularlywell suited for use in LiDAR systems, optical communications systems,optical coherence tomography and other medical imaging systems,three-dimensional imaging and sensing applications, and the like.

An illustrative embodiment in accordance with the present disclosure isa beam-steering system that includes a lens and a programmable verticalcoupler array that includes (1) a 2D array of mechanically activeintegrated-optics-based couplers and (2) an integrated-optics-basedswitching network for controlling which coupler is energized.

Each vertical coupler of the 2D array includes a grating structureformed in an integrated-optics waveguide, where the waveguide andgrating are configured such that the optical energy of a light signalpropagating through the waveguide is launched into free space by thegrating.

The switching network receives a light signal at an input port of a buswaveguide that is optically couplable with each of a plurality of rowwaveguides via a different MEMS-based optical switch that has an OFFstate and an ON state. In its OFF state, a light signal received at theswitch remains in the bus waveguide and passes through the switch withsubstantially no optical energy being lost. In its ON state, the lightsignal is completely transferred from the bus waveguide to itsrespective row waveguide. Each switch is configured such that the busand row waveguides are optically isolated from one another when theswitch is in its OFF state to mitigate leakage between them at theswitch.

Each row waveguide is also optically couplable with each coupler in acorresponding row of the coupler array by another MEMS-based opticalswitch. In the OFF state of each row-waveguide switch, a light signalpropagating through the row waveguide remains in the row waveguide andpasses through the switch with substantially no optical energy beinglost. In its ON state, the light signal is completely transferred fromthe row waveguide to its respective coupler.

The lens is arranged to receive the optical energy launched intofree-space by each coupler and convert the received optical energy intoa collimated free-space output beam. The output beam is directed along apropagation direction that is based on the x and y coordinates of thevertical coupler relative to the optical axis of the lens.

In some embodiments, only a single vertical coupler can be energized ata time. In some embodiments, the switching network enables a pluralityof vertical couplers to be energized at a given time. In someembodiments, the switching network is completely non-blocking, therebyenabling each vertical coupler to be energized regardless of the stateof any other vertical coupler.

In some embodiments the arrangement of the lens and coupler array iscontrollable.

An embodiment in accordance with the present disclosure is abeam-steering system (100) comprising: a lens (102) having an opticalaxis (A1) and a focal plane (FP1); and a programmable vertical couplerarray (104) comprising: a substrate (114); an array of couplers (112)that is a two-dimensional array characterized by a center point (CP1)and having a plurality of coupler rows (CR) and a plurality of couplercolumns (CC), each coupler of the array thereof including a couplerwaveguide (402) and a vertical-coupling element (408) that is configuredto launch optical energy received from the coupler waveguide into freespace; a bus waveguide (202) disposed on the substrate, the buswaveguide having a first input port (IP1) for receiving a first lightsignal (120); a plurality of row waveguides (204) disposed on thesubstrate; and a switching network (110) that is operative forcontrolling the propagation of a first light signal (120) from the firstinput port to any coupler of the array thereof; wherein the lens andprogrammable vertical coupler array are arranged such that the lensreceives the optical energy launched by each vertical-coupling elementof the plurality thereof and directs the optical energy an output axisthat is based on the position of that vertical-coupling element withinthe programmable vertical coupler array and a first relative position ofthe lens and the programmable vertical coupler array in at least onedimension.

Another embodiment in accordance with the present disclosure is a methodfor steering an optical beam, the method comprising: (1) providing alens (102) having an optical axis (A1) and a focal plane (FP1); (2)locating a programmable vertical coupler array (104), the programmablevertical coupler array comprising: an array of couplers (112) disposedon a substrate (114), the array of couplers being arranged in atwo-dimensional array characterized by a center point (CP1) and having aplurality of coupler rows (CR) and a plurality of coupler columns (CC),each coupler of the array thereof including a coupler waveguide (402)and a vertical-coupling element (408) that is configured to launchoptical energy received from the coupler waveguide into free space; abus waveguide (202) disposed on the substrate, the bus waveguide havinga first input port (IP1); a plurality of row waveguides (204) disposedon the substrate; and a switching network (110) that is operative forcontrolling the propagation of a first light signal (120) from the firstinput port to any coupler of the array thereof; (3) arranging the lensand programmable vertical coupler array such that the lens receives theoptical energy launched by each vertical-coupling element of theplurality thereof and directs the optical energy an output axis that isbased on the position of that vertical-coupling element within theprogrammable vertical coupler array and a first relative position of thelens and the programmable vertical coupler array in at least onedimension; (4) controlling the switching network to direct a first lightsignal from the input port to a first coupler of the array thereof suchthat the first coupler provides a second light signal (120′) based onthe first light signal to the lens, the first coupler being located at afirst position (x1,y1); and (5) collimating the second light signal anddirecting it along an output axis (A2) that is based on the firstposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B depict schematic drawings of side and top views of anillustrative embodiment of a beam-steering system in accordance with thepresent disclosure.

FIGS. 1C-D depict schematic drawings of perspective views of anexemplary beam-steering system in different beam-steering states inaccordance with the present disclosure.

FIG. 2 depicts an operational schematic drawing of a coupler array inaccordance with the illustrative embodiment.

FIG. 3A depicts a schematic drawing of a top view of MEMS optical switch206.

FIGS. 3B-C depict schematic drawings of perspective views of arepresentative MEMS optical switch 206 in its “off” and ON states,respectively.

FIG. 4A depicts a schematic drawing of a top view of an exemplaryMEMS-controlled vertical coupler in accordance with the illustrativeembodiment.

FIGS. 4B-C depict schematic drawings of a sectional view ofMEMS-controlled vertical coupler 212 in its “off” and ON states,respectively.

FIG. 4D depicts a schematic drawing of a top view of an alternativeembodiment of a MEMS-controlled vertical coupler in accordance with thepresent disclosure.

FIGS. 4E-F depict schematic drawings of MEMS-controlled vertical coupler212A in its “off” and ON states, respectively.

FIG. 4G depicts a schematic drawing of MEMS-controlled vertical coupler212B.

FIG. 5 depicts an alternative programmable coupler array in accordancewith the present disclosure.

FIG. 6 depicts another alternative programmable coupler array inaccordance with the present disclosure.

FIG. 7 depicts a schematic drawing of a side view of an alternativebeam-steering system in accordance with the present disclosure.

DETAILED DESCRIPTION

FIGS. 1A-B depict schematic drawings of side and top views of anillustrative embodiment of a beam-steering system in accordance with thepresent disclosure. Beam-steering system 100 includes lens 102,programmable coupler array 104, and controller 106. System 100 isconfigured to receive input light signal 120, collimate its opticalenergy as free-space output beam 108, and steer the output beam througha three-dimensional volume. In the depicted example, light signal 120 isa continuous wave (CW) signal; however, system 100 is operative forvirtually any light signal (e.g., frequency-modulated continuous wave(FMCW) signals, LiDAR signals, light pulses, and the like).

Lens 102 is a simple convex-convex refractive lens having optical axisA1 and focal length, f, which defines focal plane FP1. In someembodiments, lens 102 is a different type of lens, such as a compoundlens (e.g., a telecentric lens, etc.) or other multi-element lensconfigured to, for example, correct one or more aberrations or otherwiseimprove optical performance. In some embodiments, lens 102 is aplano-convex lens. In some embodiments, lens 102 is a cellphone lens,which are typically low cost and can enable mobile systems. In someembodiments, lens 102 is a diffractive element, such as a diffractivelens, holographic element, metasurface lens, and the like.

Programmable coupler array 104 (hereinafter referred to as coupler array104) includes switching network 110 and vertical couplers 112(1,1)through 112(M,N) (referred to, collectively, as couplers 112). Verticalcouplers 112 are arranged in a two-dimensional array comprising couplerrows CR-1 through CR-M (referred to, collectively, as coupler rows CR)and coupler columns CC-1 through CC-N (referred to, collectively, ascoupler columns CC).

In the depicted example, switching network 110 and couplers 112 aremonolithically integrated on substrate 114; however, in someembodiments, one or more elements of programmable coupler array 104 arelocated on substrate 114 using a different integration method, such asbump bonding, multi-chip module packaging, etc.

In the depicted example, substrate 114 is a silicon substrate. The useof a silicon substrate enables the straight-forward inclusion ofintegrated circuits and/or other circuitry that can augment thecapabilities of coupler array 104. In some embodiments, such on-chipcapability includes electronics for signal modulation, phase shifting,photodetectors, processing, memory, signal conditioning,pre-amplification, energy scavenging and/or storage, and the like. Insome embodiments, the entire electronics functionality of a LiDAR systemis monolithically integrated on substrate 114.

Controller 106 is a conventional controller that is configured tocontrol the positions of lens 102 and coupler array 104 in each of thex-, y-, and z-dimensions via a positioning system, such as ahigh-precision, multi-axis positioning system, voice coils,piezoelectric actuators, MEMS actuators, and the like. Controller 106 isalso operative for controlling the state of switching network 110 and,therefore which coupler or couplers of the coupler array are energized.In some embodiments, controller 106 is at least partially integrated oncoupler array 104.

It should be noted that, although the present disclosure is directedtoward beam steering applications, the teachings disclosed herein arealso applicable to steerable receivers (i.e., receivers whose receivingdirection is controllable), as well as transceivers that comprise both abeam-steering transmitter and a steerable receiver.

In the depicted example, lens 102 and coupler array 104 are arrangedsuch that they are concentric and the separation, s1, between them isequal to the focal length, f, of lens 102. As a result, the plane ofcouplers 112 is substantially located at focal plane FP1 and opticalaxis A1 is centered on the arrangement of couplers 112, thereby definingcenter point CP1. In some embodiments, lens 102 is located such that thelens and coupler array are separated by a distance other than the focallength of the lens and/or such that optical axis A1 is not centered onthe arrangement of couplers 112 of the coupler array.

In the depicted example, controller 106 is optionally configured to scanlens 102 along scan direction SD1 to control the lateral alignment oflens 102 and coupler array 104 in each of the x- and y-dimensions. Suchlateral scanning capability enables output beam 108 to be smoothly movedbetween angles dictated by the fixed positions of each coupler withinthe coupler array, thereby realizing a greater number of resolvablespots than possible with a fixed-position system. In some embodiments,controller 106 is further configured to control the vertical separation,s1, between the lens and coupler array, thereby enabling output beam 108to be focused at different points in space. It should be noted that thelateral alignment between the lens and coupler array can be controlledby moving only lens 102, only coupler array 104, or by moving both thelens and coupler array.

Switching network 110 includes row switch 116 and column switch 118,which collectively control the distribution of the optical energy oflight signal 120 throughout the programmable coupler array. In thedepicted example, switching network 110 is configured to direct all ofthe optical energy of light signal 120 to only one coupler 112.Switching network 110 is described in more detail below and with respectto FIG. 2.

Each of couplers 112(i,j), where 1=1 through M and j=1 through N,comprises a diffraction grating that is integrated into the structure ofan integrated-optics waveguide (i.e., a “coupler waveguide”) in couplerarray 104 and configured such that its output light signal 120′ ischaracterized by output axis A2, which is substantially aligned with ageometric line between its respective coupler and the center of lens102. In some embodiments, it is preferable that at least one diffractiongrating of couplers 112 is a blazed grating to achieve high efficiency.In addition, in the depicted example, each of couplers 112 ischaracterized by a large dispersion angle such each of light signals120′ substantially fills the clear aperture of lens 102. It should benoted that the design of each coupler 112 is typically based on itsposition with coupler array 104.

By virtue of the alignment of output axis A2 with the center of lens102, light signal 120′ illuminates a larger portion of the aperture ofthe lens, which mitigates the divergence angle of output beam 108 in thefar field and increases the resolution with which output beam 108 can besteered.

Each coupler 112(i,j) is configured such that it can be switched betweenan ON state and an OFF state. In its ON state, coupler 112(i,j) isoptically coupled with input port IP1 such that its grating structurereceives light signal 120 and scatters its optical energy into freespace as light signal 120′(i,j). In its OFF state, coupler 112(i,j) isoptically decoupled from input port IP1 and its grating structure doesnot receive light signal 120. Preferably, each coupler 112 is designedto correct for aberrations of lens 102. It should be noted that manydifferent designs for the grating element of coupler 112 are within thescope of the present invention, including one-dimensional gratings ortwo-dimensional gratings.

Lens 102 receives light signal 120′(i,j) at a distance from optical axisA1 that depends on the position of signal 112(i,j) within coupler array104. As a result, every light signal emitted by a different verticalcoupler is collimated and steered along a different output axis A2(i,j)by lens 102.

FIGS. 1C-D depict schematic drawings of perspective views of anexemplary beam-steering system in accordance with the present disclosurein different beam-steering states. Beam-steering system 100A is anexample of beam steering system 100 in which programmable coupler array104 includes only nine couplers 112A (i.e., couplers 112A(1,1) through112A(3,3)), which are arranged in a 3×3 array. Furthermore, it should benoted that, in FIGS. 1C-D, each of couplers 112A(1,1) through 112A(3,3))is an example of an alternative coupler—specifically, a conventionalvertical grating coupler—having an emission pattern that realizes arelatively narrower lights signal propagating along a propagationdirection that is substantially normal to the plane of coupler array104, as discussed below and with respect to FIG. 7.

FIG. 1C shows system 100A in a beam-steering state in which only coupler112(1,1) is in its ON state. As a result, coupler 112(1,1) receiveslight signal 120 and launches it into free space as light signal120′(1,1). Lens 102 receives light signal 120′(1,1), collimates it, anddirects it along output axis A2(1,1) as output beam 108(1,1). Outputbeam 108(1,1) propagates along output axis A2(1,1), which is oriented atangles θ_(x1) and θ_(y1). Angles θ_(x1) and θ_(y1) are angles in the x-zand y-z planes, respectively, relative to optical axis A1. Angles θ_(x1)and θ_(y1) are given by the formulas: θ_(x)=−tan⁻¹(x/f) andθ_(y)=−tan⁻¹(y/f), where f is the focal length of lens 102 and (x,y) isthe coordinate of the energized grating coupler in the x-y plane (i.e.,the focal plane of the vertical coupler array) relative to center pointCP1.

FIG. 1D shows system 100A in a beam-steering state in which only coupler112(3,3) is in its ON state. As a result, coupler 112(3,3) receiveslight signal 120 and launches it into free space as light signal120′(3,3). Lens 102 receives light signal 120′(3,3), collimates it, anddirects it along output axis A2(3,3) as output beam 108(3,3). Outputbeam 108(3,3) propagates along output axis A2(3,3), which is oriented atangles τ_(x2) and τ_(y2).

FIG. 2 depicts an operational schematic drawing of a coupler array inaccordance with the illustrative embodiment. Coupler array 104 includesswitching network 110, couplers 112, bus waveguide 202, and rowwaveguides 204-1 through 204-M.

As depicted in FIG. 2, coupler array 104 in an exemplary switchconfiguration in which MEMS optical switch 206-1 and column switch array208-1 are each in their ON states, while all other MEMS optical switches206 and column switch arrays 208 are in their OFF states (as discussedbelow). As a result, light signal 120 is diverted from bus waveguide 202into row waveguide 204-1 by MEMS optical switch 206-1 and then from rowwaveguide 204-1 into coupler 112(1,1) by column switch array 208-1.

Each of bus waveguide 202 and row waveguides 204-1 through 204-M(referred to, collectively, as row waveguides 204) is a single-moderidge waveguide having a core of single-crystal silicon. In the depictedexample, the bus and row waveguides are coplanar. In some embodiments,at least one of the bus and row waveguides is a multimode waveguide. Insome such embodiments, the multi-mode waveguide includes a large widthand is configured such that its fundamental mode can be excited toreduce optical loss.

Although the depicted example includes bus and row waveguides (and shuntand coupling waveguides, as discussed below) that are silicon-basedridge waveguides, in some embodiments, a different waveguide structure(e.g., rib waveguides, etc.) and/or a different waveguide materialsystem is used for at least one waveguide. For example, the use ofdielectric-based waveguides, such as silicon-nitride-core waveguides,can realize systems having lower optical loss and/or increased opticalpower-handling capability (peak or average), which can mitigatenonlinear effects, and the like.

Switching network 110 includes row switch 116 and column switch 118.

Row switch 116 is a 1×M switch that includes MEMS optical switches 206-1through 206-M (referred to, collectively, as MEMS optical switches 206),which are independently controllable 1×2 integrated-optics-based MEMSswitches for controlling the optical coupling between bus waveguide 202and row waveguides 204-1 through 204-M, respectively.

FIG. 3A depicts a schematic drawing of a top view of MEMS optical switch206.

FIGS. 3B-C depict schematic drawings of perspective views of arepresentative MEMS optical switch 206 in its “off” and ON states,respectively.

MEMS optical switch 206 includes a portion of bus waveguide 202, aportion of row waveguide 204, shunt waveguide 302 and MEMS actuator 304(not shown in FIGS. 3B-C).

In the depicted example, the portions of bus waveguide 202 and rowwaveguide 204 are arranged such that there is no waveguide crossingbetween them. As a result, very low optical insertion loss can beachieved, as well as substantially zero optical cross-talk between thewaveguides. In some embodiments, however, the two waveguide portionsintersect at a crossing point, preferably such that they are orthogonalto mitigate leakage of bus waveguide 202 into row waveguide 204 whenMEMS optical switch 206 is in its OFF state. In some embodiments, buswaveguide 202 includes multi-mode interference (MMI) region and tapersleading into and out of the MMI region. In some embodiments, buswaveguide 202 and row waveguides 204 are formed in different planesabove their common substrate.

Shunt waveguide 302 is a waveguide portion that extends between ends306-1 and 306-2. Shunt waveguide 302 is analogous to bus waveguide 202and row waveguides 204; however, shunt waveguide 302 is configured to bemovable relative to the bus and row waveguides.

Ends 306-1 and 306-2 (referred to, collectively, as ends 306) arealigned directly above waveguide portions 308-1 and 308-2, respectively,where waveguide portions 308-1 and 308-2 (referred to, collectively, aswaveguide portions 308) are portions of bus waveguide 202 and rowwaveguide 204, respectively.

Although not depicted in FIGS. 3A-C for clarity, typically, shuntwaveguide 302 also includes projections that extend from its bottomsurface to establish a precise vertical spacing between ends 308 andwaveguide portions 308 when MEMS optical switch 206 is in its ON state.

MEMS actuator 304 is an electrostatic MEMS vertical actuator that isoperative for controlling the vertical position of shunt waveguide 302and ends 306 relative to waveguide portions 308-1 and 308-2. MEMSactuator 304 is described in more detail below and with respect to FIGS.4A-C.

Although MEMS optical switch 206 includes an electrostatic MEMS verticalactuator in the illustrative embodiment, it will be clear to one skilledin the art, after reading this Specification, how to specify, make, anduse any actuator suitable for controlling the separation between ends306 and waveguide portions 308. Actuators suitable for use in thepresent invention include, without limitation, vertical actuators,lateral actuators, and actuators that actuate both vertically andlaterally. Further, actuators in accordance with the present inventioninclude, without limitation, electrothermal, thermal, magnetic,electromagnetic, electrostatic comb-drive, magnetostrictive,piezoelectric, fluidic, pneumatic actuators, and the like.

When MEMS optical switch 206 is in its unswitched (i.e., “off”) state,shunt waveguide 302 is held at a first position in which ends 306-1 and306-2 are separated from waveguide portions 308-1 and 308-2 by distanced1. Distance d1 has a magnitude that is sufficient to ensure thatsubstantially no optical energy transfers between ends 306 and theirrespective waveguide portions. As a result, light signal 120 bypassesMEMS optical switch 206 and continues to propagate, substantiallyunperturbed, through bus waveguide 202.

When MEMS optical switch 206 is in its switched (i.e., “on”) state,shunt waveguide 302 is moved to a second position in which ends 306 areseparated from waveguide portions 308 by distance d2, thereby definingdirectional couplers 310-1 and 310-2. Distance d2 is determined by theheight of the projections on the bottom of the shunt waveguide and has amagnitude that enables the optical energy of light signal 120 tosubstantially completely transfer from waveguide portion 308-1 into end306-1 at directional coupler 310-1 and from end 306-2 into waveguideportion 308-2 at directional coupler 310-2. As a result, light signal120 is substantially completely switched from bus waveguide 202 into rowwaveguide 204.

It should be noted that MEMS optical switch 206 is merely one example ofan integrated-optics-based MEMS optical switch. Additional examples ofMEMS switches suitable for use in accordance with the teachings of thepresent disclosure are described by T. J. Seok, et al., in “Large-scalebroadband digital silicon photonic switches with vertical adiabaticcouplers,” Optica, vol. 3, no. 1, p. 64, January 2016, as well as inU.S. Patent Publication No. 20160327751 and International PublicationNo. WO2018/049345, each of which are incorporated herein by reference.MEMS switches such those described in these publications offer manyadvantages for programmable coupler arrays in accordance with thepresent disclosure relative to prior-art beam-steering systems. Inparticular, such switches have significant lower optical loss thanconventional electro-optic or thermo-optic switches, their opticalcrosstalk (<−60 dB) and power consumption (— 10 microwatts) are severalorders of magnitude lower than conventional switches, and they canoperate in digital mode. These advantages enable beam-steering deviceshaving relatively higher throughput (i.e., lower optical insertion loss)and relatively higher resolution (i.e., greater density of gratingcouplers) than possible in the prior art, as well as simple digitalcontrol.

Returning now to FIG. 2, column switch 118 is a 1×N switch that includescolumn switch arrays 208-1 through 208-N (referred to, collectively, ascolumn switch arrays 208).

In the depicted example, each column switch array 208 includes Msubstantially identical MEMS optical switches 210, each of which isanalogous to MEMS optical switch 206; however, each MEMS optical switch210 is configured to control the optical coupling between a respectivecoupler 112 and a row waveguide 204. Each MEMS optical switch 210 andits associated coupler 112 collectively defines a MEMS-controlledvertical coupler 212.

In the depicted example, all of the MEMS optical switches 210 of eachcolumn switch array 208 are “ganged together” such that they are allcontrolled with the same control signal. As a result, each column switcharray 208 simultaneously controls the optical coupling between all Mcouplers 112 in its respective column of coupler arrays 104 and theirrespective row waveguides. Such a switch array configuration isparticularly advantageous for beam steering system having large numbersof couplers (e.g., an M×N array where each of M and N is 1000 or more),which would require M×N control signals if each coupler were addressedindividually. For large systems, the number of electrical input/output(I/O) would quickly exceed standard electrical packaging limits. The useof switch arrays, such as column switch arrays 208, however, cansignificantly reduce the number of electrical control signals requiredby enabling a “row-column” addressing scheme that reduces the number ofcontrol signals from M×N to M+N.

In the ON state of each MEMS-controlled vertical coupler 212, its MEMSoptical switch 210 optically couples its respective row waveguide 204with its respective coupler 112. As a result, when light signal 120 ispropagating through that row waveguide, its optical energy is divertedto its coupler 112. In the OFF state of each MEMS-controlled verticalcoupler 212, its MEMS optical switch 210 does not optically couple itsrespective row waveguide and coupler; therefore, light signal 120remains in the row waveguide and bypasses that coupler.

FIG. 4A depicts a schematic drawing of a top view of an exemplaryMEMS-controlled vertical coupler in accordance with the illustrativeembodiment. MEMS-controlled vertical coupler 212 comprises MEMS opticalswitch 210 and coupler 112.

FIGS. 4B-C depict schematic drawings of a sectional view ofMEMS-controlled vertical coupler 212 in its “off” and ON states,respectively. The sectional views shown in FIGS. 4B-C are taken throughline a-a depicted in FIG. 4A.

MEMS optical switch 210 includes a portion of coupler waveguide 402,which is operatively coupled with MEMS actuator 404.

Coupler waveguide 402 is analogous to shunt waveguide 302 and isconfigured to convey light from movable end 406-1 to fixed end 406-2,where vertical-coupling element 408 is located, thereby defining coupler112. In the depicted example, vertical-coupling element 408 is adiffraction grating that is configured to direct its optical energytoward the center of lens 102 when optical axis A1 is aligned withcenter point CP1. In some embodiments, at least one of vertical-couplingelement 408 includes a different optical element suitable for providinga desired output light signal 120′. Optical elements suitable for use invertical-coupling element 408 includes, without limitation, prisms,holograms, two-dimensional grating structures, diffractive lenses,diffraction-grating elements, refractive lenses, angle-etchedwaveguide-facet mirrors, angle-etched waveguides, angled mirrors, andthe like.

At movable end 406-1, coupler waveguide 402 is attached to MEMS actuator404.

At fixed end 406-2, coupler waveguide 402 is physically attached to apair of anchors 410, which are rigid elements that project up fromunderlying substrate 114. Since the coupler waveguide is affixed torigid structural elements in this region, its height above the rowwaveguide 204 is fixed.

MEMS actuator 404 is analogous to MEMS actuator 304, described above,and includes struts 412, electrodes 414, and tethers 416, which areconnected to another pair of anchors 410.

Struts 412 are substantially rigid elements that connect movable end406-1 to each of electrodes 414.

Electrodes 414 are located above a matching pair of electrodes disposedon substrate 114 (not shown) such that a voltage applied between the twopairs of electrodes give rise to an electrostatic force that pulls theelectrodes, struts, and movable end toward the substrate, therebyreducing the separation between coupler waveguide 402 and row waveguide204.

Tethers 416 are “spring-like” elements that are flexible in thez-direction but substantially rigid along the x- and y-directions. Theflexibility of tethers 416 enable the motion of movable end 406-1relative to row waveguide 204.

When MEMS actuator 404 is in its unactuated state, movable end 406-1 isseparated from row waveguide 204 by distance d1. As a result, the twowaveguides are not optically coupled, as discussed above and coupler 112is in its OFF state.

When MEMS actuator 404 is in its actuated state, movable end 406-1 isforced downward such that it becomes separated from row waveguide 204 bydistance d2, which is determined by the height of projections 418. As aresult, the two waveguides collectively define directional coupler 420,which enables substantially all of light signal 120 to evanescentlycouple into coupler waveguide 402 and propagate to grating element 408.The optical energy of the light signal is then launched into free-spaceby grating element 408 and coupler 112 is in its ON state.

It should be noted that the MEMS-controlled vertical coupler 212 ismerely exemplary and that myriad alternative designs for MEMS-controlledvertical coupler 212 are within the scope of the present disclosure.

For example, in some embodiments, no coupler waveguide is included inMEMS-controlled vertical coupler 212 and grating element is disposed ona MEMS actuator 404 itself.

FIG. 4D depicts a schematic drawing of a top view of an alternativeembodiment of a MEMS-controlled vertical coupler in accordance with thepresent disclosure. MEMS-controlled vertical coupler 212A includes MEMSactuator 404, grating element 408, platform 422, and coupler waveguide424.

Platform 422 is a substantially rigid structural element formed at thecenter of the MEMS actuator. Platform 422 includes coupler waveguide424, which is analogous to the movable portion of coupler waveguide 402.

FIGS. 4E-F depict schematic drawings of MEMS-controlled vertical coupler212A in its OFF and ON states, respectively. The sectional views shownin FIGS. 4E-F are taken through line b-b depicted in FIG. 4D.

When MEMS actuator 404 is in its unactuated state, movable end 406-1 isseparated from row waveguide 204 by distance d1. As a result, the twowaveguides are not optically coupled and coupler 112 is in its OFFstate.

When MEMS actuator 404 is in its actuated state, row waveguide 204 andcoupler waveguide 424 collectively define directional coupler 426, whichcouples optical energy from the row waveguide directly into gratingelement 408, which then emits the energy into free space.

In some embodiments, MEMS-controlled vertical coupler 212 includes a rowwaveguide and coupling waveguide that lie in the same plane andswitching is realized using a movable shunt waveguide, as describedabove.

FIG. 4G depicts a schematic drawing of a top view of another alternativeMEMS-controlled vertical coupler in accordance with the presentdisclosure. MEMS-controlled vertical coupler 212B includes MEMS actuator304, row waveguide 204, coupler waveguide 424, shunt waveguide 302, andcoupler 112. MEMS-controlled vertical coupler 212B is analogous to MEMSoptical switch 206 described above and with respect to FIGS. 3A-C.

When MEMS actuator 304 is in its unactuated state, shunt waveguide isheld well above row waveguide 204 and coupler waveguide 424. As aresult, the two waveguides are not optically coupled and coupler 112 isin not energized.

When MEMS actuator 304 is in its actuated state, shunt waveguide 302 isoptically coupled with each of row waveguide 204 and coupler waveguide424, thereby defining directional couplers at each end of the shuntwaveguide. As a result, optical energy couples from the row waveguideinto the shunt waveguide and then from the shunt waveguide into thecoupling waveguide. The optical energy is conveyed by the couplingwaveguide into coupler 112, thereby energizing it such that it emits theoptical energy into free space.

FIG. 5 depicts an alternative programmable coupler array in accordancewith the present disclosure. Coupler array 500 is analogous to couplerarray 104; however, coupler array 500 is configured to direct multiplelight signal to multiple couplers 112, thereby enabling beam-steeringsystems that can simultaneously form and steer multiple output beams.

Coupler array 500 includes switching network 502 and vertical couplers112, bus waveguide 202, and row waveguides 204-1 through 204-M.

Switching network 502 includes row switch 504 and column switches 506-1through 506-M.

Row switch 504 is an L×M switch that is operative for directing any ofinput signals 120-1 through 120-L to a different one of row waveguides204-1 through 204-M.

Each of column switches 506-1 through 506-M is 1×N optical switch thatincludes N switches 510. Column switch 506-1 directs the light signal itreceives from row switch 504 to one of couplers 112(1,1) through112(1,N), column switch 506-2 directs light signal 120-2 to one ofcouplers 112(2,1) through 112(2,N), and so on.

As a result, a beam-steering system comprising coupler array 500 canprovide a plurality of independently steerable collimated output beams110-1 through 110-L.

As noted above, the number of electrical signals required can becomeproblematic for a beam system having independently controllableswitches. For example, in system 500, the number of electrical signalsrequired is N×M+L×M. In some embodiments, however, integrated electricaladdressing circuits are included to mitigate electrical packagingproblems. Such integration can be achieved via any of a wide range ofknown techniques, such as monolithic integration, hybrid integration,flip-chip bonding, and the like.

It should be noted that the architecture of system 500 is blocking inthe sense that only one coupler 112 per row can receive a light signalfrom row switch 504.

FIG. 6 depicts another alternative programmable coupler array inaccordance with the present disclosure. Programmable coupler array 600is a non-blocking coupler array suitable for use in a beam-steeringsystem configured to provide a plurality of independently steerableoutput beams. Programmable coupler array 600 is analogous toprogrammable coupler array 500; however, switching network 602 includesa row switch that is an L×M optical switch and M column switches thatare P×N optical switches.

Coupler array 600 includes switching network 602, vertical couplers 112,bus waveguide 202, and row waveguides 204-1 through 204-M×P.

Switching network 602 includes row switch 604 and column switches 606-1through 606-M.

Row switch 604 is an Lx(M×P) switch that is operative for directing anyof input signals 120-1 through 120-L to a different one of buswaveguides 204-1 through 204-M×P.

Each of column switches 506-1 through 506-M is P×N optical switchcapable of directing a light signal received on each of P row waveguides204 to any of N coupler 112. Column switch 606-1 directs the lightsignal it receives on each of row waveguides 204(1,1) through 204(1,P)to any one of couplers 112(1,1) through 112(1,N), column switch 506-2directs the light signal it receives on each of row waveguides 204(2,1)through 204(2,P) to one of couplers 112(2,1) through 112(2,N), and soon.

In other words, each row of couplers 112 is connected to Lx(M×P) switch604 through P waveguides and a P×N switch 606. As a result, any of Pinput signals can simultaneously access the grating couplers in the samerow.

FIG. 7 depicts a schematic drawing of a side view of an alternativebeam-steering system in accordance with the present disclosure.Beam-steering system 700 is analogous to beam steering system 100;however, beam-steering system 700 includes coupler array 702, whichincludes couplers that are conventional vertical-grating couplers.

Coupler array 702 includes switching network 110 and vertical couplers704(1,1) through 704(M,N) (referred to, collectively, as couplers 704).

Couplers 704 are analogous to couplers 112; however, in the depictedexample, couplers 704 are conventional vertical-grating couplersconfigured to provide direct their free-space emission (i.e., lightsignal 706) as a relatively small-divergence light signal thatpropagates along a propagation direction that is substantially normal tofocal plane FP1. As a result, light signal 706 interacts with only arelatively small portion of the clear aperture of lens 102.

Lens 102 receives light signal 706 and collimates it as output beam 708and diverts the output beam such that it propagates along output axisA3. As discussed above and with respect to FIGS. 1A-D, the angle ofoutput axis A3, relative to optical axis A1, depends on the position ofcoupler 704(i,j) within coupler array 702.

It is to be understood that the disclosure teaches just one example ofthe illustrative embodiment and that many variations of the inventioncan easily be devised by those skilled in the art after reading thisdisclosure and that the scope of the present invention is to bedetermined by the following claims.

1-23. (canceled)
 24. An apparatus comprising: a substrate; a first rowwaveguide that is disposed on the substrate; and a first verticalcoupler comprising: (i) a first coupler waveguide having a first movableend and a first fixed end that includes a first vertical-couplingelement that is immovable relative to the substrate, the firstvertical-coupling element being configured to launch optical energyreceived from the first coupler waveguide into free space; and (ii) afirst actuator that is operatively coupled with the first couplerwaveguide and configured to move the first movable end between a firstposition in which it is not optically coupled with the first rowwaveguide and a second position in which it is optically coupled withthe first row waveguide.
 25. The apparatus of claim 24 furthercomprising: a plurality of row waveguides that includes the first rowwaveguide; an array of vertical couplers that includes the firstvertical coupler, wherein each of the array of vertical couplers isoperatively couplable with a respective row waveguide of the pluralitythereof and includes: (i) a coupler waveguide having a movable end and afixed end that includes a vertical-coupling element that is immovablerelative to the substrate, the vertical-coupling element beingconfigured to launch optical energy received from the coupler waveguideinto free space; and (ii) an actuator that is operatively coupled withthe coupler waveguide and is configured to move the movable end betweena first position in which it is not optically coupled with itsrespective row waveguide of the plurality thereof and a second positionin which it is optically coupled with its respective row waveguide ofthe plurality thereof.
 26. The apparatus of claim 25 further comprisinga lens, wherein the lens and the array of vertical couplers are arrangedsuch that the lens receives the optical energy launched by eachvertical-coupling element and directs the optical energy in a directionthat is based on the position of that vertical-coupling element withinthe array of vertical couplers.
 27. The apparatus of claim 26 whereinthe lens is selected from the group consisting of a single lens, acompound lens; a telecentric lens; a telescope; and a cellphone lens.28. The apparatus of claim 25 further comprising a switching networkthat is operative for controlling the propagation of a light signal froman input port on the substrate to any vertical coupler of the array ofvertical couplers.
 29. The apparatus of claim 28 wherein the switchingnetwork is a non-blocking switching network that enables any verticalcoupler of the array thereof to receive at least a portion of the lightsignal regardless of whether any other vertical coupler of the arraythereof is receiving at least a portion of the light signal.
 30. Theapparatus of claim 24 wherein the vertical-coupling element comprises anoptical element selected from the group consisting of a diffractiongrating, a prism, a hologram, a two-dimensional grating structure, adiffractive lens, a blazed-grating element, a refractive lens, anangle-etched waveguide-facet mirror, an angle-etched waveguide, and anangled mirror.
 31. A method comprising: providing a first row waveguidethat is disposed on a substrate; providing a first vertical coupler thatincludes a coupler waveguide having a first movable end and a firstfixed end that includes a first vertical-coupling element that isimmovable relative to the substrate, the first vertical-coupling elementbeing configured to launch optical energy received from the firstcoupler waveguide into free space; and controlling the first movable endbetween a first position in which it is not optically coupled with thefirst row waveguide and a second position in which it is opticallycoupled with the first row waveguide.
 32. The method of claim 31 furthercomprising: providing a plurality of row waveguides disposed on thesubstrate, the plurality of row waveguides including the first rowwaveguide; providing an array of vertical couplers that includes thefirst vertical coupler, wherein each vertical coupler of the arraythereof is operatively couplable with a respective row waveguide of theplurality thereof and includes: (i) a coupler waveguide having a movableend and a fixed end that includes a vertical-coupling element that isimmovable relative to the substrate, the vertical-coupling element beingconfigured to launch optical energy received from the coupler waveguideinto free space; and (ii) an actuator that is operatively coupled withthe coupler waveguide and is configured to move the movable end betweena first position in which it is not optically coupled with itsrespective row waveguide of the plurality thereof and a second positionin which it is optically coupled with its respective row waveguide ofthe plurality thereof.
 33. The method of claim 32 further comprising:controlling the propagation of a light signal from an input port on thesubstrate to any vertical coupler of the array of vertical couplers;receiving optical energy launched by at least one vertical coupler ofthe array thereof at a lens that is optically coupled with the array ofvertical couplers; and directing the optical energy in a direction thatis based on the position of the at least one vertical coupler within thearray of vertical couplers.
 34. The method of claim 33 furthercomprising correcting an aberration of the lens at the at least onevertical coupler of the array of vertical couplers.
 35. The method ofclaim 33 further comprising: providing a switching network disposed onthe substrate for controlling the propagation of a light signal from theinput port to the any vertical coupler of the array of verticalcouplers, wherein the switching network is provided as a non-blockingswitching network that enables any vertical coupler of the array thereofto receive at least a portion of the light signal regardless of whetherany other vertical coupler of the array thereof is receiving at least aportion of the light signal.
 36. The method of claim 33 furthercomprising controlling the relative position between the lens and thearray of vertical couplers.
 37. An apparatus comprising: a substrate; afirst row waveguide that is disposed on the substrate; and a firstvertical coupler comprising: (i) a first coupler waveguide having afirst movable end and a first fixed end that includes a firstvertical-coupling element, wherein the first fixed end has a first fixedheight relative to the first row waveguide and the firstvertical-coupling element is configured to launch optical energyreceived from the first coupler waveguide into free space; and (ii) afirst actuator that is operatively coupled with the first couplerwaveguide and configured to move the first movable end between a firstposition in which it is not optically coupled with the first rowwaveguide and a second position in which it is optically coupled withthe first row waveguide.
 38. The apparatus of claim 37 furthercomprising: a plurality of row waveguides that includes the first rowwaveguide; an array of vertical couplers that includes the firstvertical coupler, wherein each of the array of vertical couplers isoperatively couplable with a respective row waveguide of the pluralitythereof and includes: (i) a coupler waveguide having a movable end and afixed end that includes a vertical-coupling element, wherein the fixedend has a fixed height relative to its respective row waveguide and thevertical-coupling element is configured to launch optical energyreceived from the coupler waveguide into free space; and (ii) anactuator that is operatively coupled with the coupler waveguide and isconfigured to move the movable end between a first position in which itis not optically coupled with its respective row waveguide of theplurality thereof and a second position in which it is optically coupledwith its respective row waveguide of the plurality thereof.
 39. Theapparatus of claim 38 further comprising a lens, wherein the lens andthe array of vertical couplers are arranged such that the lens receivesthe optical energy launched by each vertical-coupling element anddirects the optical energy in a direction that is based on the positionof that vertical-coupling element within the array of vertical couplers.40. The apparatus of claim 39 wherein the lens is selected from thegroup consisting of a single lens, a compound lens; a telecentric lens;a telescope; and a cellphone lens.
 41. The apparatus of claim 38 furthercomprising a switching network that is operative for controlling thepropagation of a light signal from an input port on the substrate to anyvertical coupler of the array of vertical couplers.
 42. The apparatus ofclaim 41 wherein the switching network is a non-blocking switchingnetwork that enables any vertical coupler of the array thereof toreceive at least a portion of the light signal regardless of whether anyother vertical coupler of the array thereof is receiving at least aportion of the light signal.
 43. The apparatus of claim 37 wherein thevertical-coupling element comprises an optical element selected from thegroup consisting of a diffraction grating, a prism, a hologram, atwo-dimensional grating structure, a diffractive lens, a blazed-gratingelement, a refractive lens, an angle-etched waveguide-facet mirror, anangle-etched waveguide, and an angled mirror.